Electric drive



Feb. 19, 1946. o. s. KELLOGG ELECTRIC DRIVE Filed April 3, 1945 3 Sheets-Sheet 1 v INVENTOR. Donald S. [fa/Z 6 ATTORNEYS lllllll J'IVI 47 Feb. 19, 1946. o. s KELLOGG' ,ELECTRIC DRIVE 3 Sheets-Sheet 2 Filed April 3, 1943 INVENTUR. Donald SKQZZ T AT TORNEYS Feb. 19, 1946. D. s. KELLOGG ELECTRIC DRIVE Filed April 3, 1943 I 3 Sheets-Sheet 3 INVENTOR.

ATTORNEYS AA V Patented Feb. 19, 1946 ELECTRIC DRIVE Donald S. Kellogg, Great Neck, N. Y., assignor, by mesne assignments, to The W. L. Maxson Corporation, New York, N. Y., a corporation of New York Application April 3, 1943, Serial No. 481,681

Claims.

This invention relates to an electric drive mechanism, and more particularly to adjustable speed electric drive mechanism capable underthe influence of manual control, or of low power mechanical control, of producing any desired rotary speed of a high power output member between positive limits and between negative limits.

In one aspect the invention is in the nature of an improvement upon the invention disclosed and claimed in patent application Serial No. 473,800 of Peter J. McLaren, John A. Vaughan and Macon Fry, filed January 28, 1943, for'Continuously adjustable speed electric drive. In said application disclosure is made of a double shunt power motor having oppositely effective field windings, a manual control member movable in either of two opposite directions from a neutral position to selectively influence the field circuits, speed responsive means operated by the power motor, and make and break mechanism responsive to the joint effect of the manual control member and the speed responsive means for affecting the field circuits of the motor and thereby causing the motor to assume and maintain a speed in either direction characteristic of, and

dependent upon, the position of the manual control member.

In accordance with the present invention the same ultimate result may be obtained but through improved means. The field current of a power motor is maintained substantially constant and a generator for supplying armature current to the motor is controlled to vary the voltage applied to the motor armature. Provision is desirably made of a pair of generators, together with means for operating the generators at constant speed. One of these generators desirably develops a constant voltage which is supplied to the field of the power motor while the other gen erator, which is desirably of the self-shunt type, normally develops no voltage, but is controlled in such manner that it may be caused when rendered active to build up and apply a positive or negative voltage as desired across the armature of the power motor. The control of the generator for supplying armature current to the power motor is effected through make and break. mechanism which is responsive jointly to a manual control member and to speed responsive means operated by the power motor. When the power motor has attained the speed characteristic of any selected position in which the manual control member may be held, the make and break mechanism, under the influence of the speed responsive means, acts upon the means for energizing the generator which supplies armature current' to the motor to maintain the power motor substantially at that speed.

The direction of operation of the power motor depends upon the direction of displacement of the control member from a neutral position, and the speed, of the power motor depends upon the extent of displacement of the control member from the neutral position. The speed of the power motor may be varied at will by shifting the control member.

In another aspect, the invention is in the nature of an improvement upon the invention disclosed and claimed in Patent No. 2,248,942 of William A. Black, granted July 15, 1941, for Power amplifier, and in Patent No. 2,300,626 of Peter J. McLaren, granted November 3, 1942, for Power amplifiers.

Each of the patents just referred to discloses hydraulic means for compelling a high power output member to conform substantially in direction and speed of operation to an extraneously operated low power. control member.

In accordance with the present invention, the same kind of result is attained through electrical means. Such a result may advantageously be realized in accordance with the present invention by providing a power motor together with means for maintaining substantially constant the field current of the power motor and an armature current generator controlled to vary the armature current. A follow-up control member is made differentially responsive to the output of the power motor and to the input of a low power extraneously operated rotary control member for acting upon make and break mechanism to infiuence the generator which supplies armature current to the motor.

In accordance with the form of I the invention now regarded as most advantageous, speed responsive means operated by the power motor cooperates with the follow-up control member to maintain the speed of the power motor in substantial conformity with the speed of the extraneously operated rotary control member.

In accordance with the present invention, the follow-up control member is desirably operated from the power motor and from the extraneously operated rotary control member through an electrical differential means, the electrical differential means being especially desirable for remote control purposes.

It is an object of the present invention to provide an improved manually controlled electric drive which. is capable of producing controlled rotary output speed within limits in either oi two opposite directions at the will of the operator.

It is a further important object of the invention to provide an electrical follow-up or power amplifier mechanism capable of producing high power rotary output in either direction in conrormity with a low power rotary control member.

Other objects and advantages will hereinafter appear.

In the drawings forming part of this specification:

Fig. i is a diagrammatic view illustrating an improved electric drive which embodies features of the invention;

Figure 1a is a perspective view showing the control contacts in their physical relation to one another;

Fig. 2 is a diagrammatic view illustrating an improved follow-up or power amplifier mechanism which is adapted for remote control; and

Fig. 3 is a diagrammatic view illustrating a further improved follow-up or power amplifier mechanism which fully embodies all the principles and advantages of combining the followup features of Fig. 2 with the speed control features of Fig. i.

In accordance with the disclosure of Fig. 1, provision is made of a power motor 1 comprising a field winding 2, an armature 2, and an armature shaft 4. The purpose of the illustrated mechanism is to bring about rotary operation in either direction of the shaft 4 at a desired speed within limits, the speed being variable at the will of the operator.

Any suitable prime mover, such as an electric motor 5 energized and controlled through leads 5, is operated at constant speed to drive an output shaft '3 at constant speed. The shaft 1 drives the armature 8 of a direct current selfshunt generator 9 to supply regulated current to the armature 3 of motor I. The shaft 1 also drives the armature ill of a direct current selfshunt generator H which supplies current at constant voltage to the field winding 2 of the motor I.

Current flows from armature ll! of generator H through conductors l2 and I3, shunt field winding l4, and thence through conductors I8 and 58 back to the armature. Current also flows from the armature I through conductors l1 and I8 to field. winding 2 of power motor I and thence throulgh conductors l9 and I6 back to the armature 6.

when the motor is first started, the excitation of the generator 1 1 results at the start from the residual magnetism of shunt winding I, but when the shaft 7 of motor 5 runs at its normal constant speed, the strength of the field circuit 44 attains a normal constant value and a constant voltage is applied across the field winding 2 of power motor 3.

The generator 8 normally applies no voltage across the armature 3 of power motor I, but is adapted at the will of the operator to generate voltage for transmitting current through the armature 3 of power motor I in either direction and thereby to produce output operation of the motor shaft 4 in either direction desired. The control means whereby this kind of result is secured will be described presently.

Assuming that a voltage is being, generated by the generator 9 which makes the lower brush 20 the positive terminal and the upper brush 2| the negative terminal, current will flow through conductors 22 and 22 to the armature 2 and thence through a conductor 24, a primary winding 25 of a transformer 28 and through conductors 21, 28 and 29 back to the armature 8.

The current flowing from the armature through 22 divides at 20, a portion flowing through a fixed resistor II, a conductor 32, to a field winding 32, and thence through a conductor :4 and conductors 2| and 28 back to the armaure 3.

In the case of either of the circuits just traced out, if the polarity is reversed, the direction of current flow will be reversed. but the circuit paths will be the same. The same thing holds true for other output circuits of the armature 8, and hence the assumption that the brushes 20 is the positive terminal of the armature will be adhered to for purposes of explanation unless the contrary is stated.

The generator 9 normally develops no voltage, unless one or the other of a pair of opposite pilot field windings 85 and Si is energized. Control means are provided for selectively energizing the pilot field windings l5 and 35. When the pilot field winding 25 is energized, the resultant generated current flows from the armature 8 through shunt field 22 in one direction to aid the pilot field winding 25, and when the pilot field winding 20 is energized the generated current flows from the armature 8 through shunt field winding 22 in the opposite direction to aid pilot field winding 28. Thus, the energization of pilot field winding 25 causes a voltage to be built up and applied through the armature 2 of power motor I in one direction, while the energization of pilot field winding 28 causes a voltage to be built up and applied to armature 3 of power motor I in the opposite direction. The pilot field windings I5 and 28 are also inherently inductively coupled to the field l2 and thus the energizetion of the pilot field winding 25 causes a voltage to be built up and applied through the field II in one direction while the energization of the pilot field winding ll causes a voltage to be built up and applied through the field 22 in the opposite direction.

It will be noted that rotation of the armature 3 begins as soon as any voltage is applied across the armature and that the speed of rotation of the armature I is increasing as the voltage generated by generator 8 is being developed to its maximum value. The increasing speed of armature 2 produces an increasing counter-electromotive force in the armature circuit. The design may advantageously be such that the speed of armature 3 is sufficient at any instant in relation to the simultaneously generated and applied voltage to protect the armature 3 against destructive current fiow.

The energization of the pilot fields 25 and 3' is selectively controlled by control mechanism now to be described which includes a manual control member 31.

The manual control member 21 carries a pair of contacts 28 and 29 which are cooperative, respectively, with contacts 40 and 4|. The contacts 40 and II are carried by an arm 42 which is made fast upon a shaft 43 and is normally biased to a neutral-position by a coil spring 44. The spring 44 surrounds the shaft 43, being connected at one end to the arm 42 and at the opposite end to a stationary frame member ll.

The pairs of contacts 28-40 and 28- are adapted to be selectively engaged by movement of the control member 21 in opposite directions from a neutral position to connect them in circuit with the armature ll of generator II. The generator ll, it will be remembered, has a constant voltage output so long as the shaft 1' of the motor 9 is running at its normal constant speed. Closing of contact 38 onto contact 40 completes a circuit which comprises the armature l0, conductors l2 and H, a conductor 46, which includes a fixed resistor 41, a conductor 48, the winding of a relay 49, a conductor til, contacts 89 and 38, conductor 31a, conductor ii and conductors l9 and it. This energizes relay 43. Closing of contact 39 against contact 4| completes a circuit which includes armature l0, conductors l2, l1 and 46, a conductor 52, the winding of a relay 53, a conductor 54, contacts 4| and 39, conductor 31a, and conductors 5|, l9 and it. This energizes relay 53.

The pilot field windings and 38 of generator 9 are controlled, respectively, through switch arms 55 and 58 which are responsive, respectively, to relays 49 and 53. When relay-49 is energized, switch arm 55 is drawn down into engagement with a contact 51. When relay 53 is energized,

switch arm 58 is drawn down into engagement with a contact 58. When either relay is deenergized, the associated switch arm is returned to and maintained in the elevated position illustrated in Fig. 1.

When switch arm 55 is drawn into engagement with contact 51 by relay d9, 9. circuitis estab lished from armature iii of generator it through conductors i2 and il, thence through conductor 59, pilot field winding 95, conductor 39, switch arm 55, contact 51, conductors 6i and t2, and

, thence through conductors id and It to armature it. This energizes pilot field winding 35 from generator I i. When switch arm 56 is closed upon contact 59, a circuit is established from armature l0 of generator it through conductors l2, l7 and w 59, field winding lit, conductor 53, switch arm to, contact 58, conductor 84, and thence through conductors $2, 19 and it to armature ID. This ener-- glzes pilot field winding 33 from generator H.

From what has just been said, it is evident that pilot field winding 85 is energized whenever contact 38 is closed on contact 40, and that pilot field winding 38 is energized whenever contact 39 is closed on contact 4i. Thus operation of the manual control member 31 to close contact 39 on contact 40 causes the armature 3 of power motor i to rotate in one direction, and operation of the manual control member 37 to close contact 39 on contact 4i causes the armature 3 of power motor I to rotate in the opposite direction.

When the armature 3 of power motor i is set into operation in either direction,-the armature will gain speed until a speed is attained which is characteristic of the position to which the manual control member 31 has been moved.

Taking the case in which the manual member has been operated to engage contact 38 with contact '40 as an example, the contact '38 has not merely been moved into engagement with the contact 40, but has displaced the contact 4|! together with its supporting arm 42 a definite amount, depending upon the extent to which the manual control member 3'! has been moved away from the neutral position. This deforms the spring 44, so that the spring tends to return contact 40 to its initial position with a force whose value is dependent upon the extent of displacement of the contact 40 from that position.

The shaft 43 upon which the arm 42 is made fast is the output shaft of a torque motor or galvanometer 85. The output shaft 4 of power motor I, whose speed'it is desired to control, drives a generator 68 whose voltage output is a function of the speed of the shaft 4. By connecting the generator 68 in series with the torque motor S5,'the torque motor is caused to apply a torque to shaft 43 in opposition to the torque speed. This, however, results in a slowing down of generator 58 and in a reduction of the torque exerted by torque motor 55 upon shaft 43 and. therefore, permits the spring 44 to move contact l0 back into engagement with contact 38 so that the drive is reestablished.

So long as the contact is not moved to a new position, contact 40 will move into and out of engagement with 38 in rapid alternation, leaving engagement with 98 as soon as the speed of shaft t exceeds the speed characteristic of the position ln'which the manual control member is held, and reengaging 39 as soon as the speed of shaft it falls below the speed characteristic of the position in which manual control member 31 is held. Moving the manual control member 31 to a new position readjusts the torque applied by the spring 44 and causes the shaft 4 to assume maintain a new speed characteristic of the new position of the manual control member 31.

In line with the discussion thus far given, the control described could be effected simply by connecting generator 55 in series with torque motor to. It will be noted, however, that the closin and opening of a pair of contacts 38-40 or 99-4! must energize or deenerglze a relay, which in turn closes or opens a switch for energizing one or the other of the pilot fields 35, 36, that the energized pilot field must gradually build up current in the shunt circuit field 33 of generator 9, that the current developed by generator 9 must become effective with respect to rotation of the shaft 4, and finally that the shaft 4 must influence shaft 43 through generator 66 and torque motor 55. When contact is broken, the reverse train of events must occur through the same train of elements, so that the same lag factors are present.

It has been found that the desiredv control can be effected with less lag, and more smoothly, if the torque motor 65 is controlled in part directly irom the generator 9. An increase of generator voltage will find a direct, although perhaps somewhat delayed, response in an increased speed 01' the shaft 4, and hence the element of control contributed to the torque motor 65 by the generator 9 is consistent with the element of control contributed by the generator 66, but tends to anticipate a little, and hence to make the speed responsive control contacts more promptly effective and to hold the speed of the shaft 4 more nearly to the intended average speed.

The field 33of generator 9 is, therefore, connected in series with the generator as, the circuit being traced out in one direction from the field a of generator 9 through conductors 32 and 01, secondary winding 08 of transformer 30, conductor 69. torque motor Bl, conductor I0, generator 66, and conductors II, 23 and 30 back to the field 33 of generator 3.

The purpose of the transformer is also. to make the contact control mechanism more promptly responsive than it would otherwise be. It will be noted that transformer winding 63 has more turns than transformer winding 25, and hence that the voltage induced from the primary into the secondary is relatively high as compared with the voltage induced from the secondary into the primary of the transformer 26. While changes of voltage in the secondary have relatively little effect upon the primary circuit, changes of voltage in the primary have relatively large effect upon the voltage of the secondary circuit.

When one of the pairs of contacts 30-40 or 39-45 is first engaged, the primary voltage builds up rapidly and a considerable voltage is induced in the secondary. Unless thecontrol member 3? has been set for a very low speed, however, the torque motor 85 will be ineffective to open the engaged contacts. As theoutput voltage of generator 9 increases current flow through the primary 25 increases, but since the counter-electromotive force of the power motor I is increasing. the rate of increase of current flow through the primary 25 diminishes and the induced voltage in secondary 08 falls off, the torque motor finally breaking engagement of the active contacts in response to the voltage generated by generators 8 and 65 with only relatively minor assistance from the voltage developed in the secondary 68 of the transformer 26.

When the active contacts are thus disengaged, however, the current flow through the primary diminishes and the voltage induced in secondary 53 passes through zero and becomes of opposite sign now opposing rather than aiding the voltage directly delivered by the generators 2 and 06 to the torque motor 65. Since the voltages delivered to the torque motor 65 by the generators and 86 are diminishing at the same time (be;- cause pilot held 25 is open-circuited and generator 66 is slowing down), and since the induced voltage is opposing thejdiminishing generated voltage delivered to the torque motor, the reengagement of the active contacts is effected more promptly than would be the case if the'trans former 28 were not'present. When now the contacts are reengaged with the motor running Just below the desired average speed, the current flow through the primary 25 is increased, the induced voltage in secondary 68 again aids the increasing voltage directly applied to the torque motor 60 by generators E and 60, and as the shaft 4 gains speed the active contacts are disengaged more promptly than they would be if the transformer 28 were not present. The control contacts, when the torque motor 05 is controlled by the combination oi the three voltage sources described, namely, generator 8, generator 88, and transformer 26, make and break the control circuit in very rapid alternation and produce a very fine and accurate control.

It is not necessary to the operativeness of the invention, however, that all three of the voltage sources be combined for controlling the torque motor 65, since any one of the three voltage sources, namely, generator 9, generator 00 or transformer 26 maybe used without the others or any two of them may be used in combination but without the third to eflect a practical and advantaseous control.

It will be noted that the torque motor gradu ally overcomes the torque of spring 04 so that contacts 30-40 or 33-4I are not sharply disengaged and are not separated very widely at any time. It is for this reason, as clearly brought out in pending application, Serial No. 473,318, filed January 23, 1943, for Electric drive, of Wallace A. Lauder, that the contacts 30-40 and 30- are employed merely for energizing low voltage relay 40 and 03, and that relay control switches 50 and 50 are provided in the circuits which actually include the pilot fields 30 and 30. This feature is claimed in Serial No. 473,318.

A fixed resistor 41 in series with both the relays 48 and I! limits the voltage available at the contacts 33-40 and 30-|I and thereby prevents objectionable arclng.- A condenser 13 is connected between conductors 53 and 30, and a condenser 13 is connected between conductors 00 and 63, these condensers being provided in the cir cults of the respectivepilot field windings 30 and 38 for the p pose of suppressing arcing in these circuits.

In the form of the invention diagrammatically illustrated in Fig. 2' the parts illustrated in common with Fig. l are the same as those described in connection with Fig. 1, and hence the same reference characters have been applied to corresponding parts and no detailed description will be given of such parts.

It should be noted, however, that the torque motor 05 is omitted and that the circuit elements for applying voltage to the torque motor 6! from all three of the voltage sources illustrated in Fig. l are omitted, there being no generator 00, no transformer 26, and no connections from the generator 9 to the torque motor 65.

The mechanism of Fig. 2 is designed to make the output of power motorshaft 4 conform in direction of operation, substantially in speed of operation, and substantlallyin extent of operation to the direction, speed and extent of operation of a low torque rotary control member which may be located at a remote point. The direction, speed and extent of operation of shaft 4 may be different from the direction, speed and extent of operation of the lower torque control member, but conformity requires only that. a

uniform law of relationship be maintained.

The shaft 43, instead of being the output member of the torque motor 65, is simply mounted with freedom for rotation in a stationary bearing member IOI, subject to the restraint of spring 44. The member 31 is made fast on a shaft I02 which is driven from an alternating current, selfsynchronous differential I03.

An alternating current, self-synchronous transmitter I 04 i driven by the output shaft] of power motor I and connected to the differential I03. A similar low torque control transmitter I0! is operated manually as by a crank I00, or in any other desired manner, at a remote point and is connected to the differential I03.

Self-synchronous transmitters and self-synchronous differentials are well known per se, the illustrative devices being of the type manufactured and sold by the General Electric Company under the name of Selsyn."

Conductors I01 and I00, connected to a source of alternating current (not illustrated) are connected through single phase primary windings I00 and H0 of the stator III of transmitter Ill. The conductors I01 and II! are also connected through sinsle phase primary windings 1 I2 and ill or the stator H4 or transmitter IN. A rotor ring ill of transmitter IN is fast upon thev shaft 5 and is mechanically driven by the shaft. Each rotor .I I5 carries three identical and equally spaced windings. These windings are connected to one another and they. are connected respectively to three correspondingly spacedand correspondlngly located windings upon a stator ring H8 oi diflerential I 03. The latter windings are connected to one another through a common point. Similarly, a rotor ring H1 of transmitter it! has three identical and equally spaced windings. These windings are connected to one another and they are connected respectively to three correspondingly spaced and correspondingly located windings upon a rotor ring 8 or the differential I03. The latter windings are connected to one another through a common point. The rotor ring 8 is fast upon the shaft Hi2 and drives the shaft 102.

The eil'ectlve operation of the transmitters I04 and I08 and the diilrential W3 is precisely the same as the operation of a mechanical dlfierential gear in which the input arms correspond to rotors I I5 and I I1 and the output arm corresponds to rotor H8, the extent of operation of the output arm being equal to the diiierence of operation of the input gears. The extent of operation of the shaft 102 is, therefore, equal to the difference of the extent of operation of the shaft i and the shaft H9 upon which the rotor H'l'is iisedly mounted.

In the beginning the motor shaft 4 is stationmy and locks transmitter IN stationary, so that there is no transmission from the transmitter IM to diflerential i513. The input from the remote, low torque, conhol transmitter m5 operates, therefore, with full effect upon shaft 402. This produces engagement of one of the pairs of contact 38-t9 or tit- H, say the former pair, and causes the power motor I to set the shaft 4 into operation and, in turn, causes the transmitter Hi l to transmit electrical impulses to the diil'erential we. The impulses thus transmitted by Hi l are applied to the differential M3 in the opposite sense from those transmitted by the low torque remote control transmitter, hut until the shaft 4 has acquired the speed of the remote control transmitter. or a predetermined relationship to the speed or the remote control transmitter, the influence of the remote control transmitter will exceed the influence of the transmitter 05 and the contacts til-89 will be displaced farther and farther away from their initial positions against a progressively increasing torque of the pring 44.

As soon as the speed of the shaft l exceeds that of the remote control transmitter, the contacts $8 and 39 will tend to return toward their in-- itial positions and the spring M will cause the contact it to follow the contact 38.

when the contact 40 has been restored by the spring M to its initial position, any further recession of the contact 38 breaks engagement between 40 and St. The power motor I thereupon begins to slow down with the consequence that the influence of the transmitter. I04 upon the differential I03 is diminished. If the operation or the remote control transmitter is continued at uniform speed the remote control transmitter will again very quickly regain its ascendency over the transmitter I04 and engagement between contacts 38 and MI will be reestablished.

The making and breaking of engagement between contacts 38 and 40 will occur in rapid a1- ternation, thereby maintaining the speed of shaft 4 at the same average speed as the remote tions above and below the average speed.

Should the transmitter NM so far overrun the remote control transmitter. as to cause not only disengagement of contacts 38 and All but the endown, the engagement of ti with 39 will he very quickly broken, and the normal operation already described will be resumed. When the remote control transmitter is brought to rest the motor i will slow down substantially in conform-' ity with it and will come to rest after having substantially conformed in the extent of its oporationto th extent of operation of the low torque remote control transmitter.

()peration oi the low torque remote control transmitter in the opposite direction will produce exactly the same kind of operation of the power motor I and the control contacts as that which has just been described, but the rotation of the power motor will he in the opposite direction, and

instead of the contacts 33 and d0 the active contacts, the contacts 39 and M will he the active contacts.

In his. 3 disclosure is made all a Zollow up or amp ti r mechanism which combines the lectures of Figs. 1 and 2. All oi the parts illustrated in 3 are illustrated either in Fig. 1 or in 2. corresponding reference nuals have applied and no further detailed description will he given.

it is to noted, however; that the torque motor control is combined with the iollow up control of differential llli, the shaft 33 being the output shait oil torque motor as Fig. 1.

lil'ils arrangement constitutes definite improvement upon the arrangement disclosed in Fig. 2, since it results in a smoother and more uniform conformity of the speed of shaft d to the speed of the low torque remote control transmitter.

when, through initial operation or the remote control transmitter the contact '33 is moved to displace contact Ml against the torque of spring 5, power motor I is set into operation. This, besides exerting the influence through transmitter lil upondifierential 463 which has been already described, causes voltage to be transmitted to the torque motor 65 iron: generators 8 and $58 and transformer 25 in the manner described in connection with Fig. 1.

The torque motor as applies a torque which at first compensates in part the torque of spring 44. Now, when the speed of shaft 4 exceeds that of the remote control transmitter, and the contact 38 starts to return toward initial position, the

contact dd does not follow the contact 38 all the way to the original position of contact 40,. because it is arrested and thereby caused to break eneasement with 38 in the position in which torque motor or, exactly balances spring 45. Power motor 4 thereupon starts to slow down so that contact 38 is caused through the differential action. to he carried back toward engagement with contact Ml. At the same time the torque exerted by torque motor to begin to diminish so that contact Mi moves toward engagement with contact 38 under the influence of spring 44. The result is that the contacts are very quickly reengaged in control I transmitter, subject to slight and rapid 'fluctua-.

' that of Fig. 2 is employed.

they continue to be engaged and reenga'ged in rapid alternation with the contact 40 maintaining substantially the average position determined" by the average speed of the shaft 4. The response is substantially more prompt, and as a consequence the operation of shaft 4 is substantially smoother when an arrangement-like thatof Fig.

3 is employed than when an arrangement like As in the instance the structures previously described in connection with-Fig. l and Fig, 2, the principle of operation is the same in either direction.

' I have described what I-believe to be the best embodiments of my invention. I do not'wish, 'however, to be confined to the embodiments shown, but what I desire to secure by Letters Patent is set forth in the appended claims. Iclaim:

1, In an elect. c drive, the combination with a powermotor, of means for corltinuously'supplying field current to the motor, a generator connected to supply armature current to the motor but normally having no output, said generator including an armature, a main. field in shunt with the low torque control member and operative upon the pilot field exciting means for controlling and starting and stopping of generator excitation in accordance with the difference of extent of operation or the low torque control member and the power motor.

' 4'. In an electric drive, the combination with a power motor, of means for continuously supplying field,current to the motor, a generator connected to supply armature current to the motor but normally having no output, said generator including an armature,- a main field in shunt with thearmature through a resistor, and a pair of pilot fields of opposite efifect inductively coupled to the main field, means for driving the generator,

manually operated control means for selectively exciting the pilot fields to cause the generator to build up and apply voltagein'one direction or the other across the motor armature, and speed responsive means operated by the motor and 0perative upon the generator'excithig means for interrupting excitation of the generator when the motor speed exccedsa predetermined value characteristic of the position of the manually operated control means and, Ior reestablishing excitation of the generator when the motor speed falls 'below such vaiue.

2. In an electric drive, the combination with a power motor, of means for continuously supplying field current to the motor, a generator connected to supply armature current to the motor but nor--' mally having no output, said generator including an armature, a main field in shunt with the armatore through a resistor, and a'pair of pilot fields of opposite eficct inductively coupled to the main field, means for driving the generator, mean for causing excitation of the pilot fields to make the generator effective to generate output voltage;-a low torque control member, and difi'erential mechanism difierentially responsive to operation oi! the motor and operation of the low torque control member and operative upon thegenerator exciting means for controlling the starting and stopping of pilot field excitation in accordance with the difierence or extent of operation of the low torque control member and the power motor.-

3. In an electric drive, the combination with a power motor, oi means for continuously supplying field current to the motor, a generator connected to supply armature current to the motor, but normally having no outputsaid generator including an armature, a main field in shunt with the armature through a resistor, and a pair of pilot fields of opposite efiect inductively coupled to the main field, means for driving the generator, means for selectively exciting the pilot fields -to cause the generator to build up and apply voltage in one direction or the other across the power motor armature, a low torque control member, and differential mechanism differentially respon-- sive to operation of the motor and operation of the armature through a resistor, and a pair 0! pilot fields of opposite eil'ect inductively coupled to'the main field, means for driving the generator, means for exciting the pilot fields to make the generator effective to generate output voltage. a low. torque control member, difierential mechanism differentially responsive to operation of the motor and operation of the low torque control member, speed responsive means operated by' the motor, and contact means responsive Jointly to the difi'erential mechanism and to the speed responsive means and operative upon the pilot field exciting means to control the generator output voltage and thereby to cause the motor to conform in speed and substantially in phase to the operation of the low torque control member.

5. Inan electric drive, the combination with a power motor, of means for continuously supplying field current to the motor, a generator connected to supply armature current to the motor but normally having no output, said generator including an armature, a main field in shunt with the armature'through a resistor, and a pair of pilot fields of opposite effect inductively coupled to the main field, means for driving the generator, means for selectively exciting the pilot fields to cause the generator to build up and apply voltage in one direction or the other across the motor armature, a low torque control member, difierential mechanism differentially responsive to operation of them'otor and operation of the low torque control member, speed responsive means operated by the motor, and contact means responsive Jointly to the differential mechanism and to the speed responsive means and operative upon the pilot field exciting means to control the generator outbut normally having no output, said generatorincluding an armature, a main field inshunt with the armature through a resistor, and a pair of pilot fields of opposite efiect inductively coupled to the main field, means for driving the generator, means for'exciting the pilot fields to cause the generator to build up and apply voltage across the motor armature, an extraneously operable control member, and contact means responsive in part to the operation of the motor and in part to operation of"the extraneously operable control member and operative upon the pilot field exciting means to control the generator output and thereby to control the motor operation.

7. In an electric drive, the combination with a power motor, or a first constantvoltaze generator for supplying substantially constant field current to the motor, a second generator for building up and supplying armature current to the motor but normally having no output, means for driving said generators at substantially constant speed, said second generator having a self-shunt field and a pair of pilot fields of opposite efiect inductively coupled therewith, circuit meansfor connecting the first generator to excite said pilot fields alternatively, an extraneously operable control member, speed responsive means operated by the motor, and contact means responsive in part to said speed responsive means and in part to the operation of the extraneously operable control member and operative upon the pilot field circuit means to control the output of the second generator and thereby to control the motor operation.

8. In an electric drive, the combination with a power motor, of means for continuously supplying field current to the motor, a first generator for building up and supplying armature current to the motor, but normally having no output, said generator including an armature, a main field in shunt with the armature through a resistor, and a pair of pilot fields of opposite effect inductively coupled to the main field, means for driving the generator, a torque motor,. a contact carrying controlmember operable thereby, a second cooperative contact carrying control member operable to effect engagement of contacts carried by the respective control members and to displace the first control member, spring means responsive to such displacement to maintain the contacts in engagement with one another with a bias whose value is a function of the extent of displacement, means for supplying a voltage to the torque motor for producing a torque in opposition to said bias for operating the first control member to disengage said contacts when the bias is overcome,

power motor, and means responsive tosaid contacts for controlling the excitation of the first generator and for thereby controlling the operation oi the motor.

' coupled to the main field, means for driving the comprising a second generator, operated by the ment with one another with a bias whose value.

is a function of the extent of displacement, means for supplying a voltage to the torque motor for producing a torque in opposition to said bias for operating the first control member to disengage said contacts when the bias is overcome, comprising the main field of said generator, and means responsive to said contacts for controllin the excitation of said generator and for thereby controlling the operation of the motor.

10. In an electric drive, the combination with a power motor, of means for continuously supplying field current to the motor, a first generator for building up and supplying armature current to the motor, but normally having no output, means for driving the generator, a torque motor, a, contact carrying control member operable thereby, a second cooperative contact carrying control member operable to effect engagement of contacts carried by the respective control members and to displace the first control member, spring means responsive to such displacement to maintain the contacts in engagement with one another with a bias whose value is a function or the extent of displacement, means for supplying a voltage to the torque motor for producing a torque in opposition to said bias for operating the first control member to disengage said contacts when the bias is overcome, comprising the field of the first generator, a second generator operated by the motor, and a transformer having its primary winding in series with the armature or the first generator, and means connecting the field of the first generator, the armature of the second generator and the secondary winding of the transiormer in series with the torque motor, and means responsive to closing and opening of said contacts for starting and stopping excitation oi the first generator and for thereby controllin the operation of the motor.

DONALD S. KELLOGG.

Certificate of Correction Patent No. 2,395,000.

February 19, 1946.

DONALD S. KELLOGG I It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Pa e 6, second column, -lme 3,

claim 3, for and starting read the starting; e

' be read with this correction therein that t case in the Patent Ofice.

and that t c said Letters Patent should same may conform to the record of the Signed and sealed this 30th day of April, A. D. 1946.

[snap] LESLIE FRAZER 7 First Assistant Commissioner of Patents. 

